In one of the gloomiest predictions about the fallout from a breakup of the euro, Citigroup's chief economist on Thursday warned a collapse of the currency will result in years of a global depression that could send unemployment spiking above 20% in the West.

The comments, from Citigroup chief economist Willem Buiter, underscore the growing concern that policymakers won’t be able to forge a credible solution that will keep the currency union intact.

Buiter, previously a professor at the London School of Economics, said the ensuing chaos caused by the unlikely event of a disorderly sovereign default and exit by all five periphery nations would trigger a financial catastrophe and global depression. The disaster, he said, would send GDP plummeting more than 10% and unemployment in the West surging to 20% or more.

“If Spain and Italy were to exit, there would be a collapse of systemically important financial institutions throughout the European Union and North America and years of global depression,” Buiter wrote.

Thankfully, Buiter sees little chance of these worst-case scenarios actually coming to fruition. He forecasts a 5% or lower chance of a disorderly default and exit by all five periphery states.

Likewise, Buiter believes the likelihood of an exit by Germany and other fiscally strong countries is even less likely, attributing a less than 3% probability of such an event. That’s a good thing because he believes this outcome would perhaps be even more disastrous and extremely messy from a legal standpoint.

Still, the financial markets appear to be bracing for at least the possibility that the eurozone will no longer have 17 nations.

Hurt by comments from the ECB, the euro slumped nearly 1% against the dollar and fell below $1.33 on Thursday. Individual European bank stocks like Deutsche Bank (DB) and Barclays (BCS) suffered steep selloffs as well.

According to The Wall Street Journal even some central banks are take precautionary steps to prepare for life without the euro, including central banks in Ireland, Greece, England and Switzerland.

If the only nation to leave the currency and suffer a disorderly sovereign default was Greece, Buiter said it would be “manageable” because it accounts for just 2.2% of euro-area GDP.

Ultimately, Buiter said the potential for economic ruin should present a compelling argument for keeping the eurozone intact as much as possible.

“The case for keeping the Euro Area show on the road would seem to be a strong one: financially, economically, and politically, including geopolitically,” he wrote.